Forty-two previously untreated patients with multiple myeloma were entered in a prospective, randomised trial comparing recombinant interferon alfa-2C monotherapy with VMCP (vincristin, melphalan, cyclophosphamide and prednisolone). Both treatment arms were comparable for the stratification variables such as paraprotein type, stage of disease, and renal function. Rec. interferon effected 14% responses and 29% minor responses, while 57 and 32% of VMCP-treated patients achieved a pathologically documented remission (P less than 0.001). The time on initial treatment was significantly shorter in the IFN group (3.2 months) than in the VMCP group (7.6 months). In four patients in the IFN arm, primary treatment had to be changed according to progressive or severe stationary disease. Since all four patients responded to second line therapy (VMCP) no significant difference has been observed between the two groups in survival (median follow-up greater than 12 months). Despite this clear superiority of the conventional four-drug polychemotherapy, there was some suggestion that IFN might be particularly active in cases with low tumor-burden (stage I, II), and light-chain or IgA paraprotein type.